mm/mmap: Use the maple tree for find_vma_prev() instead of the rbtree

mm/mmap: Use the maple tree for find_vma_prev() instead of the rbtree

Use the maple tree's advanced API and a maple state to walk the tree
for the entry at the address of the next vma, then use the maple state
to walk back one entry to find the previous entry.

Add kernel documentation comments for this API.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>